The present invention relates to photographic processing equipment. In particular, the present invention relates to an improved knife assembly for use in cutters of photographic strip materials such as photographic paper or photographic film. As used in the present application, the term "knife assembly" includes assemblies which make the single cut and those assemblies which actually punch out material of a desired shape from the photographic strip.
In commercial photographic processing operations, very high rates of processing must be achieved and maintained in order to operate profitably. To expedite the photographic processing, orders containing film of similar type and size are spliced together for developing. As many as 500 to 1000 rolls of 12, 20, and 36 exposure film may be spliced together for processing and printing purposes.
After developing, the photographic images contained in the film negatives are printed in an edge-to-edge relationship on a continuous strip of photosensitive paper by a photographic printer. The photographic printer causes high intensity light to be passed through a negative and imaged on the photographic print paper. The photographic emulsion layer on the print paper is exposed and is subsequently processed to produce a print of the image contained in the negative.
After the strip of print paper has been photoprocessed to produce prints, a photographic paper cutter cuts individual prints from the strip. The prints are then sorted by customer order and ultimately packaged and sent to the customer.
The desire for high rates of processing within commercial photographic processing operations has led to the development of extremely high speed automatic paper cutters. Automatic paper cutters capable of cutting over 25,000 prints per hour (i.e. over seven prints per second) are needed, and are being developed.
The extremely high speed requirements of newly developed automatic paper cutters places extreme demands on the knife assembly. First, mechanical stability of the knife assembly becomes extremely critical in order to obtain high blade life and relatively clean cuts of the photographic paper. Because the photographic paper has a rag content and has a polyethylene coating on its top surface, it is difficult to cut without very precise and close relationship between the fixed and moving blades of the knife assembly. It has been determined that a gap of about 0.0003 inch is a maximum gap which can exist between the fixed and moving blades and still obtain acceptable paper cuts which do not have torn or ragged edges.
The prior art knife assemblies are not capable of providing acceptable quality paper cuts with long blade life at the extremely high speeds now desired for a paper cutter. The prior art knife assemblies generally contain a great deal of flexibility or sloppiness in the drive mechanism which preclude obtaining the desired tolerances in the relationship between the fixed and moving blades. In addition, the prior art knife assemblies have been generally slow because they have used rather massive movable blades and blade mounts in an attempt to obtain stability in the system. The extremely large mass of the prior art knife assemblies makes it extremely difficult to drive the knife at high speeds with a reasonably-sized motor.